1. Field of the Invention
The present invention relates to at thin film transistor liquid crystal display (TFT-LCD), and more particularly to a TFT-LCD manufacturing process with fewer photolithography steps.
2. Description of the Related Art
Liquid crystal display (LCD) is a commonly used flat panel display technology. Owing to dielectric anisotropy and conductive anisotropy of liquid crystal molecules, molecular orientation of liquid crystals can be shifted under an external electronic field, such that various optical effects are produced.
An LCD panel is generally made up of two substrates, with a certain gap preserved therebetween, and a liquid crystal layer filled in the gap. Respective electrodes are formed on the two substrates, respectively, to control the orientation and shift of liquid crystal molecules.
A TFT-LCD panel is generally made up of a TFT array substrate and a color filter substrate. The detailed structures are described as follows.
FIGS. 1A–1E are cross-sections showing the conventional manufacturing process of a TFT-LCD. First, as in FIG. 1A, a metal layer of, for example, Mo—Al—Nd is deposited on a transparent substrate 21. The metal layer is then defined to form a gate electrode 22 by photolithography. A gate insulating layer 23 is then formed on the gate electrode 22.
Next, as in FIG. 1B, an insulating layer 24, a first semiconductor layer 25 of, for example, amorphous silicon (a-Si) and a second semiconductor layer 26 of, for example, n+ doped amorphous silicon are deposited on the transparent substrate 21 sequentially. The insulating layer 24, first semiconductor layer 25 and second semiconductor layer 26 are then defined to form an island-shaped structure.
Next, as in FIG. 1C, an Al alloy layer of, for example, Al, Al—Nb, Al—Nd, Al—Ti or Al—Si—Cu is then deposited on the transparent substrate 21. The metal layer is then defined to form a signal line 27 and a source/drain metal layer by photolithography, wherein the source/drain metal layer includes a source electrode 31 and drain electrode 32, with a channel 28, exposing the first semiconductor layer 25, formed therebetween.
Next, as in FIG. 1D, a protective layer 34 is deposited on the transparent substrate 21, covering the TFT element while exposing the contact hole 30, to protect the TFT element from erosion. The protective layer 34 is, for example, a silicon nitride layer.
Next, as in FIG. 1E, an indium tin oxide layer is deposited on the transparent substrate 21. The indium tin oxide layer is then defined to form a signal line area 36 and a pixel area 38.
FIG. 2 is a cross-section of another conventional TFT-LCD, showing the storage capacitor thereof. Manufacturing of the TFT-LCD requires six photolithography steps. First, a first metal layer is deposited on a transparent substrate 50. The first metal layer is then defined to form a gate electrode 52 by a first photolithography step. A gate insulating layer 54 is then formed on the gate electrode 52 and defined by a second photolithography step. A semiconductor layer (not shown) is then formed on the gate insulating layer 54 and defined by a third photolithography step. Next, a second metal layer is deposited on the transparent substrate 50, followed by a fourth photolithography step to form a source/drain metal layer 56. Next, a protective layer 58 and a planarization layer 60 are formed sequentially on the transparent substrate 50, covering the TFT element for protection from erosion. The planarization layer 60 and protective layer 58 are then defined by a fifth photolithography step to form a contact hole. Finally, an indium tin oxide layer 64 is deposited on the transparent substrate 50 and defined by a sixth photolithography step to form a signal line area and a pixel area.
Afterwards, fabrication of a color filter 70 and liquid crystal layer 72 is performed.
Owing to the two steps of contact-hole manufacture, up to six photolithography steps are required, lowering throughput, and increasing costs.